The publication WO 2004/082804 A1 describes a filter system for diesel fuels, which has an annular particle filter as a filter element in a filter housing. Also, an annular coalescing element is connected upstream of the filter element, which has the object to aggregate droplets of water dispersively present in the fuel into larger droplets to facilitate the water separation. The coalescing element is mounted upstream of the filter element; both components are mounted about a center pipe centrally situated in the receiving space of the filter housing, which serves to discharge the cleaned fuel.
When filtering fuel, first the coalescing element is through-flown radially from the outside to the inside, a separation of droplets of water occurring at the interior wall of the embracing filter housing, which outflow downward into a water reservoir. Subsequently, the fuel is passed radially from the outside to the inside through the filter element and the cleaned fuel is axially discharged via the center pipe.
Furthermore, it is known from the publication EP 1 326 693 B1 to through-flow an annular filter element radially from the outside to the inside, having a cylindrical clean space having a center pipe, for filtering hydraulic oil. The filter device has a bypass valve between the raw side and the clean side, which is loaded with force in the closing position by a pressure spring, which is braced at a screen housing protruding into the interior of the filter element. When opening the bypass valve, the unfiltered fluid flows through the wall of the screen housing into the clean space.